This invention relates generally to wind turbine generator apparatus, and more particularly to connection of and adjustment of propeller blades on rotary hubs of such apparatus.
In recent years, it has become apparent that conventional methods of generating electricity will soon be insufficient to meet the world's ever-growing need for electric power. Several factors, including the pollution which results from the combustion of fossil fuels, the dangers associated with the operation of nuclear reactors, and the limitations inherent in the traditional hydroelectric, as well as in the more modern solar energy approaches to the generation of electricity, have encouraged the development of alternative sources of electric power, such as the wind turbine generator.
Wind turbines convert wind energy to electrical energy in a manner analogous to the way in which the windmills of Western Europe converted wind energy to mechanical energy for pumping water or operating grinding mills. A wind turbine generally includes a rotor, which is mounted for rotation near the apex of a tower approximately 18 to 50 meters in height. The rotor acts as the prime mover for an electrical generator, which provides power through transformers and substation-controlled connections, to the local utility power grid.
Generally, wind energy projects include the installation of large numbers of wind turbine generating systems at locations having favorable wind conditions. Several of these so-called "wind farms" are located in the state of California.
A major problem which has been associated with wind energy projects is mechanical failure in existing wind turbines. It has been found that the direction of the wind is not always along the rotational axis of the rotor. Off-axis wind components cause mechanical loads on the blades that were not adequately considered when the original blades were designed. Particularly, when the wind rises along a slope to a wind turbine placed at the top of the slope, it creates an additional "yawing" (side-to-side) load. This is sometimes called "vertical flow". When the wind comes in from either side ("yawed flow"), it creates an additional "pitching" load (bottom to top or top to bottom, depending on the yawed flow direction). Although such wind turbines have "active yaw systems" which are designed to rotate in response to changes in wind direction so that the rotor always faces the direction from which the wind is blowing, it has been found in practice that the rate of yaw rotation is slow compared to the rapid and variable changes in wind direction which are common in nature. These additional loads have caused major damage in turbine systems in areas such as California.
A factor contributing to mechanical failure of existing wind turbine blades lies in the circumstance that the aerodynamic loads, which begin at the tip, are integrated along the length of the blade. Therefore, longer blades (especially those producing more energy due to increased airfoil efficiency) will have higher loads at the base or root, thus making the design of the structure more critical.
The blades also weigh on the order of 1,000-1,200 pounds each, which is considered excessive for their function by modern technology standards. These blades, or very similar designs, are used in thousands of turbines installed in California.
In the past, the propeller blades of such apparatus were bolted to the generator hubs, and it was found that such bolts tended to fail at objectionably frequent intervals. Also, there was no easy way to obtain trim adjustment of the blades about their length axes once they were bolted to the hub. Such adjustment is needed to optimize the "bite" of the angled blade into or with wind stream. There is need to overcome these problems and difficulties in a simple, efficient manner to achieve much better connection of blade root ends to the generator hub, and at the same time, to accommodate blade angular adjustment.